scummvm/common/rdft.h

/* ScummVM - Graphic Adventure Engine
 *
 * ScummVM is the legal property of its developers, whose names
 * are too numerous to list here. Please refer to the COPYRIGHT
 * file distributed with this source distribution.
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version 2
 * of the License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
 *
 */

// Based on xoreos' (I)RDFT code which is in turn
// Based upon the (I)RDFT code in FFmpeg
// Copyright (c) 2009 Alex Converse <alex dot converse at gmail dot com>

#ifndef COMMON_RDFT_H
#define COMMON_RDFT_H

#include "common/scummsys.h"
#include "common/math.h"
#include "common/fft.h"

#include "common/cosinetables.h"
#include "common/sinetables.h"

namespace Common {

/**
 * @defgroup common_rdft RDFT algorithm
 * @ingroup common
 *
 * @brief API for the Real Discrete Fourier Transform (RDFT) algorithm.
 *
 * @{
 */

/**
 * @brief (Inverse) Real Discrete Fourier Transform.
 *
 * @details Used in audio:
 *  - QDM2
 *
 * Used in engines:
 *  - scumm
 *
 *
 * It has four modes:
 *
 *   Below, n = 1 << bits
 *
 *   (I)DFT_R2C:
 *     input:
 *       n real floats
 *     output:
 *       n/2 complex floats (stored as real part followed by imag part).
 *
 *     The output represents the first half of the (I)DFT of the input.
 *     If F is the complex (I)DFT of the input, then
 *     output[0] = F[0] + i * F[n/2] and
 *     output[k] = F[k] for k = 1 .. n/2-1.
 *     Note that F[0] and F[k] are real since the input is real, and
 *     the remaining values of F can be reconstructed from symmetry if desired.
 *
 *   (I)DFT_C2R:
 *     input:
 *       n/2 complex floats
 *     output:
 *       n real floats
 *
 *     The input encodes a complex vector x of length n that has the
 *     required symmetry to have a real (I)DFT:
 *     x[0] = Re(input[0])
 *     x[k] = input[k] for k = 1 .. n/2-1
 *     x[n/2] = Im(input[0])
 *     x[k] = conj(input[n-k]) for k = n/2+1 .. n-1
 *     The output is then the real (I)DFT of x, divided by 2.
 *
 *     TODO: Is this division by 2 intentional?
 */

class RDFT {
public:
	enum TransformType {
		DFT_R2C,
		IDFT_C2R,
		IDFT_R2C,
		DFT_C2R
	};

	RDFT(int bits, TransformType trans);
	~RDFT();

	void calc(float *data);

private:
	int _bits;
	int _inverse;
	int _signConvention;

	SineTable _sin;
	CosineTable _cos;
	const float *_tSin;
	const float *_tCos;

	FFT *_fft;
};

/** @} */

} // End of namespace Common

#endif // COMMON_RDFT_H